The control and management of fluids, and particularly liquids, is a practice and requirement of nearly every aspect of present day technology. As a result, a large number of liquid flow rate control devices have been devised and are in widespread use.
Particular volumetric flow rate control devices are point control devices having structure that limits and alters liquid flow rate as a function of a single or discrete point or location of restriction. Of these types, orifice plates, needle valves, ball valves, and plug valves are all widely used fixed or adjustable flow orifice devices. Each of these devices typically has a single fixed location or point of restriction which serves to entirely or principally define the pressure drop (the differential pressure between the pressure measured at the flow input and the pressure measured at the flow output) across the device. With a given motive force applied to the liquid (by, for example, a pump, gravity, or a pressurized vessel), this restriction causes flow at the liquid output to be reduced when compared to flow produced under the same conditions in the absence of the device.
For the purposes of this disclosure, a flow control device is a discrete device, made to the purpose of defining, establishing, limiting, or varying the liquid volumetric rate of flow through it, and which allows variable or adjustable liquid volumetric flow rate as a function of its structure and a physical or geometric change within the device.
The term “flow control” can be defined as a structure or device having the intended purpose of altering, establishing or defining the volumetric flow rate of a liquid. The term “control” can be defined as a volumetric liquid flow rate defining device which is manually adjusted and invariant in its flow rate control characteristics or structure unless manually altered or adjusted. Thus, a flow rate control may be thought of as a passive volumetric liquid flow control device which is not automatically adjustable or automatically interactive with or reactive to changing conditions. The term “flow controller” can be defined as a structure or device having the intended purpose of altering, establishing or defining the volumetric flow rate of a liquid. The term “controller” can be defined as a volumetric liquid flow rate defining device that can be automatically controlled and adjusted in its flow rate control characteristics, in response to some externally derived signal, command, time, or event. Thus, a flow controller may be thought of as an active, interactive, or dynamic volumetric liquid flow control device. In instances where the distinction between a flow rate control and a flow rate controller are unimportant, either may be referred to as a flow rate control device.